The present invention relates to ice-making machines, and particularly to cube ice-making machines that have a vertical ice-forming mold and a water curtain to direct water cascading down the surface of the ice-forming mold back into a water sump.
Automatic ice-making machines have become widely used to make ice on the premises where it is used. The food service industry in particular uses such ice-making machines. For example, a restaurant needs ice to put in drinks served as part of a meal. In addition, ice is often used to cool food items. In a beverage dispenser, ice may be dispensed into a cup and may also be used to cool a cold pate that in turn cools beverage components that are dispensed and mixed in valves mounted on the dispenser.
The demand for ice at many eating establishments is hardly constant. Instead, demand peaks at meal times. Most ice-making machines are therefore mounted on ice collecting and storage bins. The ice machine can then run constantly and build up a reserve of ice. Often the reserve is built up over night, and ice machines are purchased by their size, based on the expected total daily demand for ice.
Cube ice makers and flake ice makers are both in common usage. However, cube ice is generally more desirable for cooling beverages. A common design for a cube ice-making machine includes a vertical ice-forming mold. The mold has dividers that create individual pockets. When the pockets are sufficiently filled with ice, the control system for the machine switches into a harvest cycle. The ice cubes are released from the mold. The dividers may be sloped downward toward the open front so that the ice cubes slide out of the ice-forming mold under the influence of gravity, and into the ice collection bin.
The ice-making machine also includes a sump located beneath the ice-forming mold, a water distributor above the ice-forming mold, and a pump to pump water from the sump up to the distributor. The water cascades down over the surface of the ice-forming mold. A part of the water freezes into the pockets and the rest runs off the surface of the ice-forming mold. A water curtain is placed adjacent to the ice-forming mold so that any splashing water is directed back into the sump. The bottom edge of the water curtain is bent to reach back under the ice-forming mold. This allows the front edge of the sump to be spaced behind the front of the ice-forming mold. With this design, the unfrozen water can return to the sump, but ice can fall straight down out of the ice-forming mold and into the collection bin.
The water curtain is typically suspended from pivots or hinges located near the top of the water curtain. The shape of the water curtain and location of the pivots are such that the center of gravity of the water curtain causes the sides of the water curtain to stay closed against the ice-forming mold frame while the machine is making ice. However, during the harvest cycle the water curtain can swing away as the ice is released from the ice-forming mold.
A thin bridge of ice forms over the dividers and between the individual cubes of ice. Most automatic ice-making machines allow for adjustment of the duration of the freeze cycle, which thus controls how thick this ice bridge becomes. A common control technique is to mount an ice thickness sensor so that as the ice bridge gets thicker, water running over the surface of it will contact a probe, directing the machine to automatically go into a harvest cycle. A thick ice bridge has the benefit that it helps in the harvest cycle, when water stops cascading over the front of the ice and the ice-forming mold is heated. A thick ice bridge allows the entire slab of interconnected ice cubes to be released at once. On the other hand, with a thin ice bridge, individual cubes have to each melt and drop out of their pockets, and adjoining cubes cannot help pull all of the ice out at once.
While thicker ice bridges have some benefits, there are also some drawbacks. Because ice is an insulator, the efficiency of the freezing operation decreases as the ice bridge builds, since the heat is commonly transferred out of the back of the ice-forming mold by serpentine refrigerant coils forming the evaporator section of a refrigeration system. Most importantly, many end users do not want thick ice bridges, because the slabs of ice cubes do not break into individual cubes as easily, and chunks of ice cubes frozen together are hard to dispense, scoop or fit into a cup.
One other common feature found in automatic ice-making machines is that they are designed to automatically shut down when the ice collecting bin is full. These automatic ice machines then operate around the clock, unattended. The result is hopefully a bin that is constantly full of ice, but not a machine that keeps making and harvesting ice when the bin is already full.
A common technique for shutting down the ice-making machines when the bin is full is to place a sensor, such as a magnetic reed switch, near the water curtain, and put a magnet on the water curtain. The reed switch can then determine whether the water curtain is closed. This reed switch has two uses. First, when the water curtain closes, the machine can automatically switch back into an ice-making mode from a harvesting mode. Second, if ice has built up in the bin such that the slab of ice being harvested does not fall all of the way past the bottom edge of the water curtain, the water curtain will remain open, and the reed switch will not close until ice no longer holds the water curtain open.
It is desirable that the compressor of the refrigerator system not stop and start every time ice is harvested. Therefore, it is typical to let the compressor continue to run unless the water curtain remains open for a set period of time. In prior art ice-making machines, this period of time was often set at 7 seconds. Normally, the water curtain would open and close in much shorter than 7 seconds during a typical harvest cycle. However, if the bin is full, the ice cannot fall out of the way and ice remains in the way of the water curtain to keep it from closing for more than 7 seconds. In this situation, the machine would sense a “bin-full” condition and shut down until the water curtain closed again, which could happen if the ice in the bin was removed or if it melted to the point that the pile of ice no longer supported the ice holding the water curtain open.
There have been instances when a false “bin-full” signal is generated and the ice machine shuts off even if the ice bin is not full. If it stays off for a prolonged period of time, it seriously reduces the amount of ice produced by the machine. Some end users have a high demand for ice, and when an ice machine shuts down without the bin being full, the user quickly calls and reports a malfunction. What may be worse, if the machine has shut down and no one notices it, such as over night, employees came in to work expecting to have a ready supply of ice and find the bin only partially full. By then, the machine may be running again, and the cause of the problem is therefore not discernible. However, in these instances, the end user again is not happy with the equipment. Therefore, there is a strong desire to prevent a false “bin-full” shutdown on the part of ice machine manufacturers.
Solutions to the problem have been tried in the lab, but when the solution was implemented in the field, the problem reoccurred. One piece of equipment that was prone to this problem was brought back from the field to be studied. It was determined that for some reason, cubes of ice were getting caught between the bottom edge of the water curtain and either the bottom of the ice-forming mold or the top edge of the water sump. This ice would hold the water curtain open until it melted sufficiently that it dislodged itself. Even with the ice machine being shut down, this might take several hours because the bin and ice machine are insulated and the ice in the bin keeps the temperature inside the ice-making compartment relatively cool. Of course, this situation did not occur on every harvest cycle, but it did happen frequently enough that it was a serious problem for the end user. Most ice-making machines of this same model were not being complained about. However, the number of complaints with respect to this model of machine, which had two evaporators and two ice-forming molds (a dual evaporator machine), was higher than with other models of machines.
Unfortunately, dual evaporator machines are often put into establishments where there is a high demand for ice because these machines can generally make twice as much ice per day as a comparably-sized single-evaporator machine. Thus, in the very place where it is least desirable to have a machine with a false “bin full” condition, machines most prone to this problem were being installed. Also, because both evaporators are on the same refrigeration system, if the problem occurred with either ice-forming mold, both evaporators quit freezing ice. As a result, there was an urgent need to find a solution to the problem, preferably one that could be used to retrofit ice machines already manufactured that exhibited this problem.
Another problem that has been encountered arises from the fact that most water curtains are fairly large pieces of plastic. They can be assembled by gluing smaller pieces together, but most economically they are made using vacuum forming or injection molding techniques. With such large sheets of plastic it is very difficult to get them perfectly flat once they have cooled after being molded. If the water curtain is not flat, one side may not be as close to the ice-forming mold as the other. This is known as “racking,” and can let water spray come out of one side. Also, if the water curtain is racked, the slab of ice may hit one side of the water curtain first, causing a high load on the hinge pin on that side and premature failure of that hinge pin. Further, if the ice curtain is twisted too much, the side with the magnet used to operate the reed switch may be open even though the other side is closed, shutting down the machine; or it could be the other way around, with the side having the magnet being closed even though the other side of the water curtain is open because the ice bin is full on that side. Ice then continues to be made even though the bin is full on one side, and water going down the face of the ice-forming mold may fall into the bin rather than being directed by the bottom of the water curtain back into the sump, resulting in either water falling on and freezing the cubes of ice in the bin together, or wet ice in the bin. Also, for those machines that do not add water during the freeze cycle, and go into harvest when the water level drops to a predetermined point, the loss of water will result in less ice being made in each cycle.